The US Federal Reserve is prepared to print more money to tackle America’s “grave” unemployment crisis, Ben Bernanke suggested in a speech that triggered gains on stock markets.

The Fed Chairman said that the barriers to a fresh round of quantitative easing were high but that the central bank was ready to act again if further stimulus is needed to counter America’s “daunting” economic challenges.

Speaking at the Jackson Hole symposium in Wyoming yesterday, Mr Bernanke robustly defended the Fed’s previous money-printing efforts amid political attacks and claimed that the benefits outweighed the risks to the Fed’s inflation-fighting credibility.